The present invention is related to systems for displaying video characters using bit mapped memory planes, and more particularly relates to providing character attributes to such systems.
In video terminal devices which display textual material such as used in computer systems, means are generally provided to provide visual attributes to characters in the text being displayed. These visual attributes cause a selected character or characters to blink, to have a high or low intensity, to be underlined, to be blanked out, to have a light character on a dark background, or to be reversed with a dark character on a light background. The attribute data is typically carried in the data string which carries the text to be displayed, and thus takes up one character position.
U.S. Pat. No. 3,895,374 to Williams for "Display Apparatus With Selective Text Formatting" issued July 15, 1975, discloses a system for displaying images of data characters with particular display attributes in one row of a display device and for displaying images of data characters in a succeeding row of the display device with the same display attributes. The disclosed system includes an attribute decoder for decoding an attribute character accompanying a data character.
U.S. Pat. No. 4,290,063 to Traster for "Video Display Terminal Having Means For Altering Data Words" issued Sept. 15, 1981, discloses a video display terminal having a means for converting some attribute codes to character codes to give more available character codes.
U.S. Pat. No. 4,342,989 to Watkins et al. for "Dual CRT Control Unit Synchronization System" issued Aug. 3, 1982, discloses a logic control unit wherein a substantially increased number of visual attributes per display row may be accommodated with minimal effect on data character transfer rates.
U.S. Pat. No. 4,384,285 to Long et al. for "Data Character Video Display System With Visual Attributes" issued May 17, 1983, discloses a video display system having a ROM memory for storing data characters to be displayed, means for decoding character codes to address characters in the ROM for display, and a visual attribute holding register for holding visual attribute bits to be applied to a single character or a row of characters.
U.S. Pat. No. 4,422,070 to Couper et al. for "Circuit For Controlling Character Attributes In A Word Processing System Having A Display" issued Dec. 20, 1983, discloses an attribute control having a latch for latching attribute signal information entered from the keyboard. The attribute signal information remains in the latch until the attribute latch is cleared or another attribute signal is entered from the keyboard.
U.S. Pat. No. 4,462,028 to Ryan et al. for "Access Control Logic For Video Terminal Display Memory" issued July 24, 1984, discloses a video terminal system in which the video character codes and visual attribute codes are independently applied to the video display logic.